The present invention relates to a highly resistant, granular starch, the method of making such starch, and uses thereof.
This invention relates to a highly resistant granular starch with high dietary fiber content which may be prepared by the selected heat-moisture treatment of high amylose starch and then treating the starch with amylase to obtain a highly resistant starch. Further, the invention relates to the use of this highly resistant granular starch in food products.
Starch, a complex carbohydrate, is composed of two types of polysaccharide molecules, amylose, a mostly linear and flexible polymer of D-anhydroglucose units that are linked by alpha-1,4-D-glucosidic bonds, and amylopectin, a branched polymer of linear chains that are linked by alpha-1,6-D-glucosidic bonds. Starch is digested predominantly in the small intestine by the enzyme alpha-amylase. Alpha-amylase hydrolyzes alpha-1,4-D-glucosidic bonds, but does not hydrolyze the alpha-1,6-D-glucosidic linkages, resulting in less complete hydrolysis of the amylopectin fraction.
It is known that certain starch processing operations result in the transformation of starch into starch that is resistant to pancreatic amylase, known simply as resistant starch. Resistant starch resists digestion by pancreatic alpha-amylase and absorption in the small intestine, but passes into the large intestine where it is fermented by colonic microflora to short chain fatty acids and gases. Research literature indicates that this fermentation of resistant starch by colonic bacteria has numerous beneficial effects including colonic health and reduces the chances of developing diverticulosis and colon cancer. Further, as it is not utilized until it reaches the large intestine, where it is fermented to short chain fatty acids, resistant starch has a reduced caloric value and in respect of these properties has the benefits of dietary fiber.
Resistant starch (RS) has been classified in the literature into four categories depending on the causes of resistance. RS1 is a physically inaccessible starch due to entrapment of granules within a protein matrix or within a plant cell wall. RS2 is a granular starch that resists digestion by pancreatic alpha-amylase. RS3 is a retrograded, nongranular starch formed by heat/moisture treatment of starch or starch foods. RS4 is a chemically modified starch that resists digestion by alpha-amylase and includes acetylated, hydroxy propylated, or cross-linked starches.
Various methods have been reported for producing the various types of resistant starch. These include U.S. Pat. No. 5,593,503 which describes a method of making a resistant starch of the RS2-type; U.S. Pat. Nos. 5,281,276 and 5,409,542 which describe methods of making resistant starches of the RS3-type; and U.S. Pat. No. 5,855,946 which describes a method of making a resistant starch of the RS4-type.
However, unless highly crosslinked, these resistant starches are not highly resistant and commercially resistant starches typically have a resistance in the range of about 35-65%. Due to the benefits of resistant starch, more highly resistant starches which are chemically unmodified would be important and of great value.
More highly resistant starches are known and are described for example in U.S. Pat. No. 5,051,271 and WO 90/15147. However, these highly resistant starches are nongranular.
Surprisingly, it has now been discovered that highly resistant granular starch can be prepared and that such starch has unique and useful properties.
Highly resistant granular starches may be produced which have unique and useful properties, including high resistance, high dietary fiber, a unique molecular weight distribution, a high melting temperature and a high heat of gelatinization (Delta H) indicative of excellent processing tolerance. These starches may be prepared for example by heating a high amylose starch having at least 40% amylose content by weight at a percent moisture and temperature insufficient to destroy the granular nature of the starch, and digesting the amorphous regions, e.g. by using alpha-amylase or a chemical reagent
This invention further relates to food products which contain the highly resistant granular starch with high dietary fiber content, particularly those prepared using the heat-moisture treatment as described herein.